Useful resolution - any benefit to more megapixels?

The closest comfortable viewing distance for a print is about equal to its diagonal, I believe. Held normally at that distance it subtends a little under 50 degrees horizontally at the eye. Someone with good vision has an angular resolution of about 1 arc minute (any details separated by less than that are indistinguishable). Allowing one pixel per arc minute and the usual 3:2 width to height ratio, that makes a bit less than 6 MP in total. So for normal purposes (excluding certain specialised applications) what is the point of 15, 18, 20 MP? I'm not saying that there isn't any benefit, but I wonder whether more could be gained for the most common applications by applying the technological improvements that have gone into these dense sensors to something of lower resolution, and getting better sensitivity, dynamic range and colour (and smaller files). I guess that this has been discussed plenty of times before, but I'm curious as to where the tradeoffs are, especially as some of you have experience with this range of resolutions.

Another thing that occurs to me is that diffraction limiting kicks in at wider apertures with denser sensors. The diffraction limited linear resolution (smaller is better) is proportional to the focal length and inversely proportional to the aperture diameter (i.e. it is proportional to the F-number, which is another application of that useful quantity). So in order to take full advantage of a denser sensor you need a wider relative aperture. This would mean that applications that require a large depth of field, and therefore a small aperture, like landscape and high magnification (macro) benefit the least from very high sensor resolution, even if essentially perfect optics were available. I'm not saying that higher resolution makes things worse in this respect in the final output, but beyond a certain point it can't make things any better, and there might be other drawbacks. Even with a 10 MP APS-C sensor diffraction starts to have an effect at not a lot narrower than F8.

Will

Cropping is the immediate, obvious answer. If you have an 18MP sensor, but only need 6MP to print, then you can crop up to 66% of you picture out, giving you plenty of room to adjust the composition, or a kind of post production 3x crop factor to zoom in further on that shy animal you couldnt get closer to. Additionally a little extra resolution helps make sure that the image comes out nice and sharp once scaled down to a standard print. This is before you get into the obvious things like larger prints, where you might want it to stay sharp when you get closer to look at a detail rather than the whole image; and viewing on a computer, gigapixel images become faster or higher resolution when your sensor provides you more per frame to begin with.

with respect to the comment about having larger sensor pixels to improve noise etc rather than just pushing up the MP, look at the popularity of the D40.

finally:

MARKETING

unfortunately people can see Megapixels, they dont understand sensor size, which i suspect is why the sensors on even high end bridge cameras are dwarfed by even a 4/3 sensor. However now that superzoom cameras are comming into popularity, some manufacturers are starting to push the lenses on their bridge cameras beyond their limits to sell the optical zoom number, with things like 30-600mm (i belive i have seen 26x optical zoom) lenses appearing that are too long for hand-held, and soft anyway once you do get them on a tripod.

Anyway, i ramble too much, someone elses turn...

In my opinion the "Mega Pixel war" was pretty much declared a draw when they passed 8MP. I'm currently at 21 with the 1Ds3 and I've got 44" canvas prints hanging side-by-side from both the 1Ds3 and my old 20D (8MP) - and you really can't see much of a difference (if any).

As alluded to above though - it does allow for more agressive cropping - although, if one has to crop that agressively, then it's a sure-sign that the composition wasn't optimal to begin with:eek:

Personally, I'd rather have less pixels and more dynamic range.

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Originally Posted by Colin Southern

if one has to crop that agressively, then it's a sure-sign that the composition wasn't optimal to begin with

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or that you couldnt afford the extra few hundred mm of focal length

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Originally Posted by wjh31

or that you couldnt afford the extra few hundred mm of focal length

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This is certainly what drives me to crop agressively :(

I agree that in most cases having lots of MPs is not that beneficial. However if one does a fair amount of manipulation, that higher pixel density can be helpful. I also went from an 8MP 30D to a 21MP camera and, other than much larger file sizes and bringing my XT system to its knees, there is not a great deal of difference in the printed result.

However I am afflicted with "pixel-peeper syndrome" and there the difference is very evident, but I digress. Yes, higher MP counts with the resultant higher sensor Nyquist frequencies are really starting to push the limit of even the "pro" class lenses. This combined with the harsh reality of diffraction will limit the "super-sharp" DOF to much less than we had been satisfied with in the past. Maybe the only way to get super sharp, large dof images will be to use panoramic techniques, with many shots per image!

Bring on the camera system with a dynamic range of 14 - 16 stops and multiple sensors and physical apertures making it possible to take a huge pano with great dof with the single click of a button:D

The cropping argument is certainly valid to some extent, but I've just never found it compelling because of the sheer inefficiency involved. To get a zoom equivalent of 3x by cropping you lose 89% of the pixels. One one hand that could be an argument for having lots of pixels to begin with; on the other hand it could be an argument for fundamentally changing the original composition. To me cropping is more a matter of shaving a bit off the edges than trying to do a digital zoom.

Anyway I'm glad that my back-of-the-envelope calculation wasn't too far from reality. Given the choice of a lot more pixels or ISO performance that is better by a stop or so along with greater DR, I am pretty sure that I would choose the latter. But useful improvements in areas like AF subsystems generally seem to come bundled with megapixels at the moment.

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Bring on the camera system with a dynamic range of 14 - 16 stops and multiple sensors and physical apertures making it possible to take a huge pano with great dof with the single click of a button:D

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One thing for sure is that our audience, ie. the general public, is becoming more aware of quality images with the highest possible dynamic range and deepest black levels. Just look at flat panel TV displays and see what I mean. People now expect quality images and are becoming cognoscenti of them. No one wants a new TV with only 2,000/1 dynamic range. They expect an order of magnitude and greater performance.

So pixel peeping seems to have become more popular with pros and amateurs alike.

That being said, the demand for more perfect, higher dynamic range/lower noise photographs can only increase. The manufacturer that can offer a reasonably affordable camera with say three more stops of noise-free performance, will capture a huge market, and so I would expect to see lots of innovation in this area. It will be fun to watch.

I tend to agree with you. I've heard arguments about print quality and how you should multiply the size, say 11x14 by 300 dpi to get the megapixel count you need. I've just printed some 11x14 B&W from my 10mp Nikon D80 -- at Costco, no less -- and they are stunning even though the math says they're under-powered in the megapixel count, even if you stare at them up close. And I know I can do better with a higher quality printing service.

OTOH, I keep reading articles claiming that at least for B&W film, digital still doesn't produce the same sharpness/resolution, so I wonder if that's part of the megapixel drive, at least for FF/PRO.

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Originally Posted by eNo

I tend to agree with you. I've heard arguments about print quality and how you should multiply the size, say 11x14 by 300 dpi to get the megapixel count you need.

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Personally, I think that the people who insist on 300 dpi being a "minimum" requirement should do a little maths of their own.

Lets go metric for the sake of ease of discussion; there's more-or-less 25 millimeters in an inch, so 300 dpi would equate to 12 pixels in one millimeter, squared (because we're talking a 2 dimensional image) ...

... which equates to potentially 144 tone changes in a single square millimeter.

I don't know about anyone else, but my eyes just couldn't resolve 144 tone changes in a single millimeter at ANY viewing distance, and probably not even with a magnifying glass. So to my mind this 300 dpi thing is just silly.

Just my 10c worth!

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Originally Posted by will_c

So for normal purposes (excluding certain specialised applications) what is the point of 15, 18, 20 MP?

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FWIW one of the reasons I like lots of pixels is because I like photographing things that are too small to see clearly with the naked eye. Springtails mostly but there's plenty other small beasties that fascinate me.

Does using your camera as an expensive magnifying glass count as a specialised application? ;) I'm often shooting at (well and truly) diffraction limited apertures but still find the extra resolution can help show details I wouldn't see otherwise.

6MP for prints? Has been plenty for the ones I've seen from my 300D....certainly plenty for the 12x8's I put on my wall :)